The present disclosures relate to compound semiconductor structures, and more particularly, to III-V compound semiconductor devices with a surface layer in access regions having charge of polarity opposite to channel charge and method of making the same.
The existence of charge on gate oxide surfaces presents a problem in certain types of semiconductor devices, in particular, implant free MOSFETs. The existence of negative charge on gate oxide surfaces may not affect the workfunction of a gate metal of implant free MOSFETs to a large extent if the charge density is not excessively high. However, the existence of negative charge on gate oxide surfaces causes depletion between the gate and source/drain contacts of the implant free MOSFETs. Such depletion causes excessive sheet resistance in an underlying semiconductor layer and degraded device performance, both of which are undesirable.
In addition, with respect to prior known III-V MOSFETs, performance and scaling limitations are imposed by the coupling of threshold voltage and saturation current via sheet carrier concentration in the prior known III-V MOSFETs.
Accordingly, there is a need for an improved method and apparatus for overcoming the problems in the art as discussed above.
The use of the same reference symbols in different drawings indicates similar or identical items. Skilled artisans will also appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.